When we got our portable air conditioner several years ago, we got one with a double hose because it was supposed to be much more efficient to have the hot air go out the window through its own hose and the outside-temperature air come in to be cooled through its own hose. But now, all the portable models I see at the store are only single hose ones. Have they become more efficient, or is it just an aesthetic decision? I don’t see how it could be more practical, as you have to block off the same height of window opening to vent one hose or two.
The main point of the hose is not to bring air in (or out either, really), it is to vent heat. In most circumstances, it is most efficient for the A/C to suck in room air (already cooler than outside, once the machine has been running a little while) and to blow it out again further cooled. The heat goes into the air in the hose, which I believe, from the units I have seen, simply diffuses away into the outside air. You do not want to suck in the hot outside air, which will take more energy to cool to an acceptable temperature (and if the air outside is already cooler, you are better off just opening the windows, and using a fan).
What?
A duel duct system is more effecient.
On a duel duct system you are using hot outside air to cool the condencer. Yes the machine will have a slightrly higher head pressure requiring slightly more power to give you the same discharge air temperature on the evaporator.
On a single pipe system cool air from the room is used to cool the condencer. Lower head pressure. But as an example if the outside air is 90 degrees and the inside air is 75 degrees; then 75 degree air is pulled from the room and blowned accros the condencer and vented to the outside. And 90 degree air is pulled from outside through air leaks into the building. This air will need to be cooled to 75 degrees to maintain temperature. that is a major heat gain.
Try reading again? 
I agree… it recirculates the “already cooled” air.
I still say what? Recirlating “already cooled” air across the condencer and outside is a waste of energy.
On a two duct system the air sucked in is not cooled but absorbs heat from the condencer. On a one pipe system room air is sucked to absorb heat from the condencer and in both cases is blown outside. The heat of condensation does not just symply diffuses out the pipe but is discharged with the air from the condencer.
On the evaporator side of both types air is pulled from the room blown across the evaporator coils where it is cooled and discharges into the room. there are two seperate air flows and a more efficient unit will keep both completely seperate.
No, read it again, again. No air goes out of or into the room. The already cooled air in the room is sucked into the unit, cooled further, and blown back out into the room again. The outside air in the hose gets heated up further and diffuses away.
It would be, but you made up the “and outside” bit yourself. That is not what I said.
The directions on the 2-hose unit I have specifically state that the cooler hose has to go outside; you can’t use it to suck up cooler room air.
I would imagine that the hose that exhausts to the outside is the discharge air from the hot side of the heat exchanger. The intake for that side is also inside the room (on the unit itself).
From my limited experience with standalone AC units (they are novelty items in the UK) they were all set up like this:
Intake A (inside room) > Cools refrigerant circuit > Hot air exhausted out of pipe outside room.
Intake B (inside room) > heat exchanger cools this air > Cool air exhausted into room.
Some of them had intakes/exhaust ducts that were away from the unit itself, to reduce the problem of the unit just cooling the corner where it sits. If you move the intake well away from the device, you don’t need quite such high fan settings to help distribute cooler air throughout the room.
According to this site that is not how it works and your way would be terribly inefficient. Heat dumped into a 5 ft long tube will not “diffuse” away very quickly without forcced convection and the temperature in the tube would rapidly approach the temperature of the coil.
no the hot air does not diffuse away. On a single pipe sistem air is blown across the condencer and discharged to the outside. Outside air does not flow two ways in the pipe. The flow is from the room across the condencer where it picks up heat, out the discharge air pipe. Now with air removed from the room that air has to be replaced. There is no migration or diffuses it if blown by a fan in one direction.
Far the bigger problem is that on a one hose system, air has to enter the room somewhere, and it does so by drifting through the house toward the system. That means the machine is generating and eating its own local cloud of cold air. To spread cool air around the machine has to throw it uphill, against the overall flow of air toward the machine. If you put an exhaust fan in your bedroom window, hot air from the rest of the house constantly moves in through your door. Well, a one hose machine is also an exhaust fan blowing room air out the window.
OK, that site is not terribly explicit, but it seems to be saying that a small amount of the room air is sucked through and vented to the outside in order to clear the heat out of the tube. That makes sense, even though, as you link says, it introduces an inefficiency by creating a negative pressure inside the room. Otherwise, that page is in accord with what I said. The type of unit where the body of the unit extends through the wall or through a window works in a similar way, but does rely on diffusion (and convection) to remove the heat, and thus does not need to suck any air out of the room, and avoids the consequent inefficiency. I can see why, if the unit has a long vent tube, diffusion might not be sufficient to carry the heat away. (On the other hand, if they are not relying on diffusion, I am puzzled as to why the vent tubes are so wide -about 6" in diameter in my experience. They are certainly not blowing air out at the sort of high rate that that would enable. I had assumed the width of the vent tube was to allow diffusion, and if it does not rely on diffusion then I don’t see why a narrower tube would not be as good or better.)
Snnipe 70E, you do not seem to be able to understand my explanations, and I do not know how to make myself any clearer (and I certainly cannot make any sense of your latest screed). I suggest you read the section on single-hose units at Baracus’s link. Perhaps you will understand that. Apart from the point about relying on diffusion to remove the heat (and its explanation as to why not being able to rely on diffusion introduces an inefficiency), it says the same as what I was trying to convey.
Window A/Cs always have a condenser fan - they never just rely on convection.
Whatever. The point is they are not blowing room air to the outside.
Have a single pipe system. Have worked with single and double pipe systems. Can not understand your problem of my explanation.
Heat is removed from a AC unit at the condencer.
air is blown across an condencer picking up heat. Are you getting that?
That air comes from a fan that pulls air from the room on a single pipe unit. the air travels across the condencer and out of the unit. It leaves the unit by traveling through the discharge duct to the out side.
Can you explain to me what part you disagree with me and can not understand.
To quote the link
“A single-hose system takes in the air from the room, cools it and puts it back into the room. A single-hose unit creates a slight negative pressure in the room it cools because it does not return all of the air it takes in from the room. A small amount is used to cool the unit and is expelled through the exhaust system. Unconditioned air from adjacent rooms is often drawn into the cooled room to compensate, and this creates a slight inefficiency in the system. A single-hose system usually cools a room down more slowly than a dual-hose system”
This link states that the air from the room that goes across the condencer is “expelled through the exhause system” ie it goes outside.
Another name for these units is a **“Move and Cool”. **This link indicates that some units are using the same fan for the condencer air and evaporator air, and I guess on the small one it is possable. On all the larger unit that I have seen there were two fans and seperate air flows.
How can you work in the business and not know how to spell “condenser?”
When I am at work I watch my spelling but at home I do not nit pick and I make mistakes with spelling often. There are reasons for my problem I can live with it, sorry for the errors.
So, what is the answer? Is it better to get a single-hose model, or two hoses?